@mixin rect($height){
  width:100%;
  position: relative;
  &>*:nth-child(1){
    width: 100%;
    overflow: hidden;
    &:after {
      content: '';
      display: block;
      margin-top: $height;
    }
  }
  &>*:nth-child(1n+2){
    width: 100%;
    height: 100%;
    position: absolute;
    top:0;
    right: 0;
    bottom: 0;
    left:0;
    overflow: hidden;
  }
}